The present invention relates to a process for the sterilization of one or more chemical products in a gaseous state for use in the treatment of materials, articles or enclosures.
Recourse to gaseous sterilization is essential for sterilizing products or articles which cannot be subjected to the elevated temperatures employed in conventional heat sterilization methods, or to high energy radiation, such as gamma rays, or to germicidal solutions, such as glutaraldehyde solutions. In general, gas sterilization is mainly carried out by exposing the surfaces to be sterilized to biocidal gases such as ethylene oxide or formaldehyde. The processes employed at present have many disadvantages.
Ethylene oxide, which is employed on a very large scale, reacts slowly and is highly inflammable. It is, moreover, highly toxic, being capable of producing mutagenic effects in exposed individuals. It has to be employed at elevated concentrations (from 500 to 2,000 mg per liter) which exacerbate the hazard, such as the presence of residues in the articles, high concentrations in the atmosphere of sterilization rooms, and environmental pollution.
Formaldehyde, whose biocidal activity has long been known, presents significantly fewer hazards than ethylene oxide, but the results obtained in the processes currently employed are highly unsatisfactory. Although, in some working conditions, sterilization cycles have been found to be effective against populations of resistant spores (B. Subtilis, B. stearothermophilus) exposed directly to formaldehyde vapor, the inconsistency of the results and the diversity of opinions which divide the users of these methods must be acknowledged. Also, a question which is being asked by hygienists is whether the apparatuses and processes currently in existence make it possible to produce sterilization or, more precisely, disinfection. Formaldehyde is generally employed in two ways, namely, either by depolymerizing paraformaldehyde by heating, or by injecting formol (an aqueous solution of formaldehyde at a strength of approximately 40%, with the addition of 5 to 10% of methanol) into a sterilizer which is, in addition, supplied with saturated steam at a pressure below atmospheric pressure. Although formaldehyde possesses a biocidal activity which is highly effective at concentrations above 5 mg per liter, and even 2 mg per liter, sterility is not always attained under these conditions of use because of the difficulty in controlling the sterilization parameters, particularly the gas concentration and relative humidity.
This random nature of sterilization with formaldehyde in the presence of steam has long been known as is evident from a study which was started in Britain in 1950 under the auspices of the Central Public Health Laboratory. In the discussion of experimental results it is stated that it was difficult to obtain reproducible results, that the effect of humidity was unclear and finally that disinfection with formaldehyde vapor is not to be attempted when any other process is available. Furthermore, the damaging role of water condensation has also been demonstrated.
Some manufacturers of apparatuses for low temperature sterilization have tried to avoid the problems due to water condensation by automatically purging condensates during the sterilization cycle. Others, aware of the wide variation in the concentration of gaseous formaldehyde during the sterilization cycle, have proposed repeated injections of formaldehyde in solution.